To assess the possibility of using aerobic denitrification (AD) bacteria with high NO2−-N accumulation for nitrogen removal in wastewater treatment, conditional optimization, as well as sole and mixed nitrogen source tests involving AD bacterium, Comamonas sp. pw-6 was performed. The results showed that the optimal carbon source, pH, C/N ratio, rotational speed, and salinity for this strain were determined to be succinate, 7, 20, 160 rpm, and 0%, respectively. Further, this strain preferentially utilized NH4+-N, NO3−-N, and NO2−-N, and when NO3−-N was its sole nitrogen source, 92.28% of the NO3−-N (150 mg·L−1) was converted to NO2−-N. However, when NH4+-N and NO3−-N constituted the mixed nitrogen source, NO3−-N utilization by this strain was significantly lower (p < 0.05). Therefore, a strategy was proposed to combine pw-6 bacteria with traditional autotrophic nitrification to achieve the application of pw-6 bacteria in NH4+-N-containing wastewater treatment. Bioaugmented application experiments showed significantly higher NH4+-N removal (5.96 ± 0.94 mg·L−1·h−1) and lower NO3−-N accumulation (2.52 ± 0.18 mg·L−1·h−1) rates (p < 0.05) than those observed for the control test. Thus, AD bacteria with high NO2−-N accumulation can also be used for practical applications, providing a basis for expanding the selection range of AD strains for wastewater treatment.

Sugarcane bagasse as a biomass solid waste has good prospects as a carbon source for biological wastewater treatment. However, it has rarely been investigated for aerobic denitrification (AD). Herein, we investigated its carbon release performance and constructed a bagasse-loaded sequencing batch biofilm reactor (SBBR) to investigate the feasibility of sugarcane bagasse as a carbon source and filler for AD bacteria to treat wastewater with low carbon–nitrogen ratios (C/N). Results showed that chemical oxygen demand (COD) leaching from sugarcane bagasse was 418.07 ± 17.05 mg/g; high-temperature and high-pressure operation had no significant effect on the carbon release performance of the bagasse. A shake-flask experiment revealed that adding sugarcane bagasse significantly enhanced the AD flora denitrification effect in low C/N wastewater; the removal process of NO₃⁻–N by AD flora followed first-order kinetics. In the SBBR inoculated with AD flora, biofilm formation on the bagasse surface was evident; the NO₃⁻–N removal rate reached 20.20 ± 4.27% after 28 operation cycles, which was significantly higher than that of the control sequencing batch reactor during the same period, and the effluent COD stabilized below 50 mg/L. The results provide a reference for AD application in the practical wastewater treatment and biomass resource utilization of sugarcane bagasse.

Research on Fe³⁺ reduction coupled to anaerobic ammonium oxidation (Feammox) and its associated processes in the moderately low-dissolved oxygen (DO) urban natural environment is lacking. To clarify seasonal and spatial variations in Feammox, iron-reducing, and anaerobic ammonium oxidation (anammox) in urban green spaces, we examined the physicochemical indices and functional genes acd, acm, Geo, and hszA in topsoils and wetland soils across four seasons. Further, we performed 16S rRNA high-throughput sequencing. The Feammox-related gene acm was detected in all topsoil samples. Season and habitat affected soil physicochemical indices influencing gene distributions. Moisture content (45.3%) and Fe³⁺ (13.3%) mediated genetic changes. Competition between Feammox and iron-reducing bacteria (IRB) lowered the distributions of acd and acm in summer and increased these in winter. The acd and acm distributions were higher in wetland soil than in forestland soil. The dominant phyla, Nitrospirota, Actinobacteriota, and Desulfobacterota, correlated positively. Network analysis revealed that the relative abundances of acd, Geo, and hszA correlated positively with Flavobacterium and Thermomonas, Subgroup_2, and Candidatus_Solibacter, respectively. Feammox, iron-reducing, and anammox microorganisms correlated positively but competition existed between certain taxa. Candidatus, Sphingomonas, and Geobacter are linked to Feammox, iron reduction, and anammox. Here, we demonstrated the theoretical feasibility of developing Feammox-based nitrogen removal technology under moderately low-DO conditions, providing a reference for elucidating the ecological contribution of Feammox in an urban green heart.

Thermal alkaline hydrolysis is a common pretreatment method for the utilization of excess activated sludge (EAS). Owing to strict environment laws and need for better energy utilization, new methods were developed in this study to improve the efficiency of pretreatment method. Direct thermal hydrolysis (TH), pasteurized thermal hydrolysis (PTH), and alkaline pasteurized thermal hydrolysis (PTH + CaO and PTH + NaOH) methods were used to treat EAS. Each method was compared and analyzed in terms of dissolution in ammonium nitrogen (NH4 + -N) and soluble COD (SCOD) in EAS. Furthermore, the removal of tetracycline resistance genes (TRGs) and class 1 transposon gene intI1 from EAS was investigated. The NH4 + -N and SCOD concentrations in EAS treated by PTH were 1.24 and 2.58 times higher than those of TH. However, the removal efficiency of total TRGs and intI1 between the groups was comparable. The SCOD concentration of the PTH + NaOH group was 4.37 times higher than that of the PTH group, and the removal efficiency of total TRGs was increased by 9.52% compared with that by PTH. The NH4 + -N and SCOD concentrations of the PTH + CaO group could reach 85.04% and 92.14% of the PTH + NaOH group, but the removal efficiency of total TRGs by PTH + CaO was 19.78% lower than that by PTH + NaOH. Thus, to reduce the financial cost in actual operation, lime (CaO) can be used instead of a strong alkali (NaOH), and pasteurized steam at 70°C instead of conventional high-temperature heating to treat EAS. This study provides a reference for the development of alkaline hydrolysis under moderate temperatures along with the removal of TRGs in EAS.